Sintering Furnace for Components Made of Sintered Material, in Particular, Dental Components

Abstract

The invention relates to a sintering furnace (1) for components (15) made of a sintered material, in particular for dental components, comprising a furnace chamber (2) having a chamber volume (VK) and a chamber inner surface (OK), wherein a heat-up device (5), a receiving space (9) having a gross volume (VB) located in the chamber volume (VK) and delimited by the heat-up device (5), and a useful region (10) having a useful volume (VN) located in the gross volume (VB), are disposed in the furnace chamber (2). The furnace chamber (2) has an outer wall (3) consisting of a plurality of walls having a wall portion (7) to be opened for introduction into the receiving space (9) of a component to be sintered (15) and having an object volume (VO). In the furnace chamber (2) the heat-up device (5) has a thermal radiator (6) having a radiation field (13) which radiator is disposed on at least one side of the receiving space (9). Said thermal radiator (6) has a specific resistance of 0.1 mm.sup.2/m to 1,000,000 mm.sup.2/m and has a total surface, the maximum of which is three times the chamber inner surface (OK). With this sintering furnace (1) a heat-up temperature of at least 1100 C. can be achieved within 5 minutes at a maximum power input of 1.5 kW.

Claims

1. A sintering furnace for components made of a sintered material comprising: a furnace chamber having a chamber volume (VK) and a chamber inner surface (OK), wherein a heating device, a receiving space having a gross volume (VB) located in the chamber volume (VK) and delimited by the heating device, and a useful region having a useful volume (VN) located in the gross volume (VB) are arranged in the furnace chamber, and wherein the furnace chamber has an outer wall including a plurality of walls having at least one wall section to be opened for introducing a component to be sintered into the receiving space, wherein the heating device in the furnace chamber contains at least one thermal radiator, which has a specific resistance ranging from 0.1 mm.sup.2/m to 1,000,000 mm.sup.2/m and a total surface area that is at most 3 times the chamber inner surface area (OK).

2. The sintering furnace according to claim 1, wherein the chamber volume (VK) of the sintering furnace is between 50 cm.sup.3 and 200 cm.sup.3.

3. The sintering furnace according to claim 1, wherein the maximum total surface area of the thermal radiator is about 400 cm.sup.2.

4. The sintering furnace according to claim 1, wherein the object volume (VO) is at most 202040 mm.sup.3.

5. The sintering furnace according to claim 1, wherein the thermal radiator can be heated in a resistive or inductive fashion.

6. The sintering furnace according to claim 1, wherein the heating device consists of graphite, MoSi.sub.2, SiC, or glassy carbon.

7. The sintering furnace according to claim 1, wherein the outer wall has a chamber inner wall that is impermeable and/or reflective to the radiation field.

8. The sintering furnace according to claim 1, wherein the thermal radiator of the heating device has a heating rate in the useful region of at least 200 K/min at 20 C.

9. The sintering furnace according to claim 1, wherein the useful volume (VN) is at most 202040 mm.sup.3 and that the dimensions of the useful volume (VN) are at most 20 mm20 mm40 mm.

10. The sintering furnace according to claim 1, wherein the thermal radiator is designed as a crucible (11).

11. The sintering furnace according to claim 1, wherein the total surface area is at least 1.0 times the chamber inner surface area (OK).

12. The sintering furnace according to claim 1, wherein the sintered material is for one or more dental components.

13. The sintering furnace according to claim 1, wherein the one or more dental components are made of ceramic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be explained with reference to the drawings. Shown are:

[0036] FIG. 1 a part of a sintering furnace according to the invention for components made of a sintered materialespecially, for dental components;

[0037] FIGS. 2A, B an inductively heatable heating device with a thermal radiator consisting of a crucible and coil;

[0038] FIG. 3 a plate-shaped, inductively-heatable thermal radiator having an integrated coil;

[0039] FIGS. 4A, B resistively-heatable heating devices with thermal radiators consisting of rod-shaped heating elements;

[0040] FIG. 5 a heating spiral as a resistance heating element;

[0041] FIG. 6 a thermal radiator consisting of a heating spiral and reflector;

[0042] FIG. 7 a thermal radiator consisting of U-shaped heating elements;

[0043] FIG. 8 a thermal radiator consisting of planar heating elements;

[0044] FIGS. 9-16 different arrangements of the thermal radiator and the useful volume in the furnace chamber.

EXEMPLARY EMBODIMENT

[0045] FIG. 1 shows a part of a sintering furnace 1, which has a furnace chamber 2 with a chamber volume VK, the walls 3 of which are provided with an insulation 4 for shielding the hot furnace chamber 2 against the environment. The chamber volume VK is in this case between 50 cm.sup.3 and 200 cm.sup.3. For heating the furnace chamber 2, a heating device 5 with two thermal radiators 6 is arranged in the furnace chamber 2. The furnace chamber 2 has a wall section 7 to be opened for introducing a component 15 to be sintered into the furnace chamber 2, which wall section in this case is the lower wall section, i.e., the bottom of the furnace chamber 2. The component 15 to be sintered has a volume of at least 101010 mm.sup.3. The maximum size of the component 15 is 202040 mm.sup.3.

[0046] The bottom 7 likewise has an insulation 4, on which a base 8 for the components 15 to be sintered is placed, which base is also designated as support 8. As support 8, cross pieces or a crucible or vertically-placed pins made of ceramic or high-melting metal, onto which the component 15 is placed, are also to be considered.

[0047] As a result of the heating device 5 or the thermal radiator 6, which, in FIG. 1, is, for example, arranged on two sides of the furnace chamber 2, there is, within furnace chamber 2, a free volume, which is smaller than the chamber volume VK and which, in FIG. 1, is indicated with a dashed line and is designated as the gross volume VB. The space that this gross volume VB occupies is the receiving space 9, into which an object 15 to be sintered can be introduced. In this case, the heating device 5 has a total surface area that is at most 2.5 times a chamber inner surface area OK. The total surface area of the heating device 5 is in this case not larger than 400 cm.sup.2. The material of the heating device 5 has a specific resistance of between 0.1 mm.sup.2/m to 1,000,000 mm.sup.2/m, wherein the heating device 5 can, for example, consist of graphite, MoSi.sub.2, SiC, or glassy carbon.

[0048] Using the thermal radiator 6 of the heating device 5, the receiving space 9 is heated, wherein at least a part of the gross volume VB of the receiving space 9 is heated in a sufficiently strong and uniform fashion. This region is designated as the useful region 10, and the volume as the useful volume VN. In FIG. 1, the useful region 10 is schematically depicted with a dot-dashed line, and a second largest dimension of the useful region 10 is drawn in as D. The size and position of the useful region 10 is determined essentially by the emission characteristics, i.e., the radiation field 13, and the arrangement of the radiator 6, wherein a placement of the radiators 6 on at least one side of the receiving space 9 ensures that the useful region 10 lies within the receiving space 9.

[0049] The object 15 to be sintered can, for example, be resistively or inductively heated. In FIGS. 2A and 2B, for example, an inductively heated thermal radiator 6 is depicted as heating device 5. The thermal radiator 6 is designed as a crucible 11made, for example, of graphite, MoSi.sub.2, SiC, or glassy carbonwith at least one circumferential coil 12 for inductive heating, wherein the emission of the crucible 11, i.e., the thermal radiation 13, is indicated by arrows. In this example, the receiving space 9 is formed by the inner space of the crucible. The useful region 10 likewise is located in the inner space of the crucible 11, wherein the ratio of the usable volume VN of the usable region 10 to the gross volume VB of the receiving space 9 is 1:1.

[0050] Even though not shown in FIG. 2A, a retort, such as a bell jar, can be provided, which is arranged in the crucible and surrounds the component 15.

[0051] The component 15 to be sintered is arranged in the inner space of crucible 11, in the receiving space 9 that coincides with the useful region 13. The distance of the object to the thermal radiator 6, i.e., to the crucible 11 in this case, is designated as d.

[0052] FIG. 3 shows a thermal radiator 6 formed from two plate-shaped elements, which is heated by means of integrated coils 12. The receiving space 9 correspondingly is located between the two plate-shaped elements. FIG. 3 furthermore shows the radiation field 13 of the thermal radiator 6 with lines. This accordingly results in a useful region 10 that is arranged in the receiving space 9 and that covers an area as homogeneous as possible of the radiation field 13 with high intensity.

[0053] The thermal radiators 6 depicted in FIGS. 4A and 4B consist of three or four rod-shaped, resistance heating elements 14 respectively.

[0054] Additional variants of resistive thermal radiators 6 and arrangements are shown in FIGS. 5 through 8. The thermal radiator 6 shown in FIG. 5 is designed as a heating spiral 16, wherein the receiving space 9 and the useful region 10 are cylindrical and arranged within the heating spiral. In FIG. 6, the thermal radiator 6 is a combination of a radiant heaterin this case, a heating spiral 16 and a reflector 17wherein the receiving space 9 and the useful region 10 are located between the heating spiral 16 and the reflector 17. FIG. 7 shows a thermal radiator consisting of two U-shaped heating elements 18 having a receiving space 9 arranged between the two U-shaped heating elements 18. In FIG. 8, a thermal radiator 6 consisting of two planar heating elements 19 is depicted. These typically have a planar emission pattern, as a result of which the useful region occupies an especially large part of the receiving space 9 located between the planar heating elements 19.

[0055] With a maximum power consumption of 1.5 kW, a heating temperature of at least 1,100 C. can be achieved with the sintering furnace 1 according to the invention within 5 minutes.

[0056] The ratio of the radiator surface area to the surface area of the chamber inner surface is specified to be at most 2.5. In specifying this value, it has been assumed that the chamber inner surface area also corresponded to the surface area of the useful volume. The considerations regarding this maximum ratio were substantially based upon an annular thermal radiator as it is formed by the shell surface of the crucible of FIG. 2A.

[0057] In rod-shaped thermal radiators as an embodiment according to, for example, FIGS. 4a, 4b, 7, it comes about that the surface of such thermal radiators can be smaller than the surface of the furnace chamber or than the surface of the useful volume. In a furnace design with rod elements as thermal radiators, the chamber inner surface is considerably larger than the useful volume, as a result of which the surface area ratios are virtually zero. If the surface of the useful volume is selected instead, a reasonable minimum ratio of the radiator surface area to the surface area of the useful volume of 0.4 results.

[0058] The useful volume is defined as the limit within which a safe burning process is possible. It has geometric dimensions which can, for example, be specified by means of the length, width, and height (lwh). If the size of the useful volume is increased, the specified ratio to the total surface area of the thermal radiator decreases. Such a furnace can, however, be operated continuously only at a lower power.

[0059] It is also conceivable that the dimensions of the thermal radiator protrude beyond the boundaries of the furnace chamber, to arrive approximately at a ratio above 2.5. With an upper limit of the ratio of 3, a sufficient compromise between the additional technical economical effort to be made and the advantage of the invention is afforded here. The lower limit of 1 limits the invention in terms of power output, compared with furnaces with smaller thermal radiators.

[0060] FIGS. 9-16 show different arrangements of the thermal radiator and the useful volume in the furnace chamber. For example, FIG. 9 shows a schematic design of a furnace 21 with a furnace chamber 22, which is delimited at the bottom, at least partially, by an inner and an outer doorstone 23, 24also called upper and lower doorstones. The doorstone is surrounded laterally by the lower wall section of the furnace chamber, which wall section is designed with multiple parts in the present case, viz., with three layers.

[0061] On the lower wall section 25 rests an annular thermal radiator 26, which is arranged in the furnace chamber 22 and which, again, is surrounded by an annular insulating wall section 27. For reasons of clarity, the coils located further outside for inductively heating the thermal radiator 26 are not shown.

[0062] Above the annular wall section 27, the furnace chamber 22 is delimited by the upper wall section 28, which is designed with multiple layers like the lower wall section 25. A thermal element 29 protrudes through the upper wall section 28 into the furnace chamber 22 and thereby also penetrates to some extent into the inner space 30 enclosed by the thermal radiator 26, and thus delimits a useful volume 31 arranged in the inner space 30, since the component arranged on the doorstone 23 and not shown must not come into contact with the thermal element 30. The surface of the furnace chamber 22 is in this case formed by the surface of the wall section 27 facing the furnace chamber, and by the top side of the doorstone 23 and the bottom side of the upper wall section 28. The annular space around the thermal element, as well as the gap between the first door element and the lower wall element, are disregarded.

[0063] FIG. 10A illustrates in detail the arrangement of the restricted useful region 31 with respect to the radiator 26 of FIG. 9, in order to compare it to a useful region 31 illustrated in FIG. 10B. The ratio of the total surface area of the thermal radiator and the furnace chamber does not change, even if the ratio of the total surface area of the thermal radiator to the surface area of the useful volume decreases from FIG. 10A to FIG. 10B.

[0064] FIG. 11 shows a thermal radiator 26, which additionally comprises a bottom 32 and a lid 33, as a result of which the total surface area of the thermal radiator 26 compared to the total surface area of the thermal radiator 26 of FIG. 9 is increased. The useful volume 31 corresponds to that of FIG. 10B.

[0065] In FIG. 12, the useful volume 31 is reduced by insulating wall sections 34, 35, wherein the thermal radiator itself remains unchanged compared to FIGS. 9 and 10A, 10B. The surface area of the furnace chamber thus also decreases, and the ratio of the total surface area of the thermal radiator and the furnace chamber increases.

[0066] FIG. 13 shows a furnace 41 with a furnace chamber 42, which, at the top and at the bottom, goes beyond the inner space 31 of the thermal radiator 43 and continues into the upper and into the lower wall sections 28, 25 so that the useful region is enlarged. The ratio of the total surface area of the thermal radiator and the furnace chamber is decreased as a result.

[0067] In FIG. 14, the useful region is further reduced, compared to the useful region of FIG. 13, by the upper and the lower wall sections 28, 25 no longer having the same inner diameter as the thermal radiator 43. The total surface area of the thermal radiator remains the same, but the surface area of the furnace chamber is reduced, compared to that of FIG. 13.

[0068] In FIG. 15, several cylindrical thermal radiators 52 (4 thermal radiators are illustrated in this case) are arranged in pairs at a distance from one another in a given furnace chamber 51, which radiators extend into the drawing plane. The useful region is located between a pair of radiators. The ratio of the total surface area of the thermal radiators 52 to the surface area of the furnace chamber 51 is smaller in comparison to the arrangement of FIGS. 9-14.

[0069] This also applies if elongated planar heating elements 62 are used in a furnace chamber 61, as illustrated in FIG. 16, instead of cylindrical thermal radiators.

[0070] The thermal radiators of FIGS. 15 and 16 can also be resistive radiators, which are heated as a result of the electrical resistance when an electrical current passes through them.